The subject invention is directed toward the art of plastic closure elements and, more particularly, to plastic closure elements or seal plugs that include a body section extending through at least one opening in at least one support or panel, an enlarged head section on one side of the support or panel, and a thermal expanding material disposed on at least one area of the closure element, the thermal expanding material being adapted to expand under the influence of temperature to seal the at least one opening.
The invention is especially well suited for incorporation in automotive body panels and will be described with reference thereto; however, as will become apparent, the invention is capable of broader application and could be incorporated in a variety of components or used as a separate fastener for many purposes.
Other closure elements made of plastic and a thermal expanding material are already known in the art such as shown in German patent number DE 40 18 425 A1. In the above prior art example, the closure element includes a hollow space defined in the body of the closure element. The hollow space is filled with at thermal expanding medium which, after installing the closure lid in a support opening, expands under the influence of temperature to thus press areas of the closing lid against adjacent areas of the support opening. This results in producing a closure of the support opening. One problem with closure elements having the above-known construction is that it is necessary to take special design and manufacturing measures in order to provide the hollow space in the body of the closure element.
In addition to the above, other closure caps are known which are made of plastic and which have, at respective opposing top and bottom ends thereof, a sealing lip, which acts upon the adjacent surfaces in the area of the support opening. Examples of this type of closure cap are DE-OS 35 12 582, DE-OS 30 11 448 and GB-PS 1354973.
One problem all of the above closure caps experience is the possibility of unintentional separation from the support opening before the thermal expanding material has had an opportunity to expand and seal the support opening and attach the closure element thereto. Thus, with the above closure caps, provisions must always be provided by means of additional fixtures or additional structural elements on the closure cap in order to ensure that the closure element remains fastened to the respective support opening until such time as the thermal expanding material has had an opportunity to expand and seal fastening the closure element to the opening.